The Plague of Thieves Affair (Carpenter and Quincannon Mysteries)

"John Quincannon has been hired by the owner of the Golden State brewery to investigate the "accidental" death of the head brewmaster, who drowned in a vat of beer. John is certain he can catch his quarry, but his partner, Sabina, is not sure she even wants to catch hers: Sherlock Holmes or, rather, the madman claiming his identity." -- Publisher's website.